1. Field of the Invention
This invention relates to a solid propellant eject motor propulsion device that provides initial boost velocity to a tube-launched missile. More particularly, the invention relates to a method to fabricate a solid propellant grain for an eject motor in a spiral wrap with air gaps between the spirally wound layers, the gaps providing good burn propagation during a short burn time, boost phase firing.
2. Description of the Prior Art
An example of the prior art is found in U.S. Pat. No. 3,159,104 which discloses a method to fabricate a solid propellant motor by utilizing alternate layers of oxidizer-rich and fuel-rich propellants, separated by, for example, metal foil, the whole rocket motor being wound in a sprial pattern, one layer upon the other; thus, spirally wrapping the composite material into the general size desired. This patent suffers in that it has layers of oxidizer-rich and fuel-rich materials, one on top of the other, with no air space between, thus the composite rocket motor need not have structure-bearing interfaces between layers of propellant. If the layers were separated by an air space, as is taught in the instant invention, then the layers would not withstand the stress imposed on the grain during firing.
U.S. Pat. No. 3,316,842 basically discloses a series of stacked discs that are individually formed and stacked one on top of the other to form a basic solid propellant motor. Each disc is comprised of a layer of a fuel comprising an aluminum metal powder and another layer of an oxidizer, such as ammonium perchlorate, the fuel and the oxidizer being separated by a metallic disc or other suitable non-metallic material. This invention is disadvantaged in that each disc is tightly compacted against the adjacent disc, thus inhibiting the burning properties of the solid propellant motor. The instant invention, having layers of fuel and oxidizer on adjacent sides of a fiberglass structural separating element, may be cured so that each spiral wrap of the composite solid propellant material has an air space between an adjacent wrap, the structural element between the layers of propellant being sufficiently strong when fully cured to support the spiral wrap with air spaces therebetween. The present invention, therefore, provides a superior fabrication method as well as providing more burning surface to affect the burning rate of the eject motor.